virtio_ring: packed: extract the logic of vring init

Separate the logic of initializing vring, and subsequent patches will
call it separately.

This function completes the variable initialization of packed vring. It
together with the logic of atatch constitutes the initialization of
vring.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220801063902.129329-21-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -1932,6 +1932,22 @@ static int vring_alloc_state_extra_packed(struct vring_virtqueue_packed *vring_p
 	return -ENOMEM;
 }
 
+static void virtqueue_vring_init_packed(struct vring_virtqueue_packed *vring_packed,
+					bool callback)
+{
+	vring_packed->next_avail_idx = 0;
+	vring_packed->avail_wrap_counter = 1;
+	vring_packed->event_flags_shadow = 0;
+	vring_packed->avail_used_flags = 1 << VRING_PACKED_DESC_F_AVAIL;
+
+	/* No callback?  Tell other side not to bother us. */
+	if (!callback) {
+		vring_packed->event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
+		vring_packed->vring.driver->flags =
+			cpu_to_le16(vring_packed->event_flags_shadow);
+	}
+}
+
 static struct virtqueue *vring_create_virtqueue_packed(
 	unsigned int index,
 	unsigned int num,
@@ -1986,11 +2002,6 @@ static struct virtqueue *vring_create_virtqueue_packed(
 
 	vq->packed.vring = vring_packed.vring;
 
-	vq->packed.next_avail_idx = 0;
-	vq->packed.avail_wrap_counter = 1;
-	vq->packed.event_flags_shadow = 0;
-	vq->packed.avail_used_flags = 1 << VRING_PACKED_DESC_F_AVAIL;
-
 	err = vring_alloc_state_extra_packed(&vring_packed);
 	if (err)
 		goto err_state_extra;
@@ -2001,12 +2012,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	vq->packed.desc_state = vring_packed.desc_state;
 	vq->packed.desc_extra = vring_packed.desc_extra;
 
-	/* No callback?  Tell other side not to bother us. */
-	if (!callback) {
-		vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_DISABLE;
-		vq->packed.vring.driver->flags =
-			cpu_to_le16(vq->packed.event_flags_shadow);
-	}
+	virtqueue_vring_init_packed(&vring_packed, !!callback);
 
 	virtqueue_init(vq, num);